The present invention relates to a wheel plate of a coupler for use in coupling a trailer and a tractor and, more particularly, to a wheel plate provided with lubricant groove device for lubricant, suitable for use in the coupler of a trailer-tractor in which coupling and uncoupling operation is not frequently made.
Systems for coupling a trailer and a tractor are divided broadly into two type conneting systems. One of these known systems is so-called semi-trailer type connecting system in which a part of the weight of the trailer is born directly by the tractor. This type of connecting system incorporates a connecting mechanism referred to as coupler. More specifically, the coupler is provided thereon with a wheel plate which, in turn, slidably carries an upper plate fixed to the lower side of the trailer. At the same time, a king pin prvided at the lower side of the trailer rotatably engages with the coupler to permit a relative pivotal movement between the tractor and the trailer. The wheel plate is provided in its upper surface with lubricant groove device for lubricant to lubricate the sliding surfaces of the wheel plate and the upper plate to smooth the relative pivotal movement between the tractor and the trailer.
In the conventional wheel plate, the lubricant groove device is composed of a combination of a circular or oval groove and a plurality of radial grooves. This form of lubricant groove device, however, has no definite theoretical support and, hence encounters the following problems. First of all, it is to be pointed out that the lubricant does not move smoothly when the trailer-tractor is steered to the left or right. In addition, this form of lubricant groove device does not permit an easy spreading and dispersion of the lubricant to the sliding surfaces. Therefore, it is often experienced that the oil film between the wheel plate and the upper plate is broken to cause an undesirable phenomenon called seizure, unless the trailer and the tractor is frequently uncoupled for application of the lubricant. As the state of the seizure is developed further, the smooth running and steering are lost to impose a danger in the running of the trailer-tractor.